Salt

On the surface, I'd say it just suggests that they share a "salt tooth", probably a genetic trait.

Symbolically? I don't know, maybe it has something to do with the practice of salting the earth to prevent the growth of crops?

Wade's upbringing and very existence has been negatively impacted by his own father -- in the sense that they share the same troubled tendency to drink and propensity for violence. When he tries to stand up to his father in the flashback, I don't think it's necessarily a coincidence that the latter remarks, "Look at him bursting out of the seams of his jeans!" In this case, he's trying to escape his jeans/genes by rebelling against the cycle of violence.

And/Or, one might suggest that genetics don't enter into it at all; that Wade's troubles have been passed down through experience. Either way, the idea of applying salt to otherwise fertile ground is a powerful one -- Wade couldn't grow up properly because his childhood had been "salted".